The present invention relates to an ink jet printer head and a piezoelectric actuator for the head, in particular, in which ink filled in a pressure chamber is jetted by converting an electric energy into a mechanical vibration energy in high efficiency.
Conventionally, a piezoelectric actuator, in which a vibration transferring plate and a piezoelectric plate having a characteristic, which is expanded and contracted by applying a voltage, are unified, has been developed and used for an ink jet printer head and a pressure pump. The piezoelectric actuator for the ink jet printer head is classified into two types. In one type, a vertical vibration of the piezoelectric plate is used, and in the other type, bending, which is generated by the vibration of the piezoelectric plate unified the vibration transferring plate, is used.
For example, a technical report, written by T. Katakura, xe2x80x9cTechnology to Make Ink Jet Printer Head High Performance xe2x80x9d Ultrasonic Wave TECHNO, 1998, pp. 33-36, describes a structure of an ink jet printer head used a piezoelectric actuator and its ink jet theory in detail.
FIG. 1 is a perspective view showing a structure of this conventional ink jet printer head and its piezoelectric actuator for this head. As shown in FIG. 1, this conventional ink jet printer head used the piezoelectric actuator consists of an upper electrode 91, a piezoelectric plate 92, a lower electrode 93, a vibration transferring plate 94, and a pressure chamber 95.
An electric energy applied to the piezoelectric actuator is converted into a mechanical vibration energy by the upper electrode 91, the piezoelectric plate 92, and the lower electrode 93. This mechanical vibration energy is transferred to liquid ink filled in the pressure chamber 95 via the vibration transferring plate 94, and is converted into an acoustic energy. This acoustic energy is converted into a kinetic energy, which is required to make ink drops hit paper, at a small hole provided on the surface of a printer head. The kinetic energy makes the ink drops jet the paper. The amount of this kinetic energy depends on the size of the mechanical displacement, generated by the mechanical vibration energy by the piezoelectric actuator, of the vibration transferring plate 94.
At the piezoelectric actuator, it is required that the energy conversion efficiency from the electric energy to the mechanical vibration energy is high, that is, it is required that the mechanical displacement of the vibration transferring plate 94 is large. This energy conversion efficiency is shown as follows: the energy conversion efficiency=the mechanical vibration energy/the applied electric energy. The larger the energy conversion efficiency is, the bigger the mechanical displacement becomes. Therefore, as shown in FIG. 1, the piezoelectric actuator, which consists of the vibration transferring plate 94, the lower electrode 93 formed on the vibration transferring plate 94, and the piezoelectric plate 92 having a long rectangle shape, disposed on the lower electrode 93, and the upper electrode 91 formed on the piezoelectric plate 92, is generally used.
However, at the conventional piezoelectric actuator mentioned above, the expanding and contracting movement in the width direction of the piezoelectric plate 92 is mainly used, and the expansion and contraction in the length direction does not contribute to the vibration. Consequently, the energy conversion efficiency from the applied electric energy to the mechanical vibration energy is very low. That is, there is a problem that the kinetic energy being sufficient to jet liquid ink cannot be obtained, because the mechanical displacement of the vibration transferring plate 94 is small.
It is therefore an object of the present invention to provide an ink jet printer head and a piezoelectric actuator for the head, in which energy conversion efficiency from an electric energy to a mechanical vibration energy is high, and its mechanical displacement of a vibration transferring plate is large. Further, by using the piezoelectric actuator of the present invention, it is easily possible to realize a thin-sized and efficient pressure pump for the ink jet printer head.
According to a first aspect of the present invention for achieving the object mentioned above, there is provided an ink jet printer head. The ink jet printer head provides a pressure chamber, which is formed in a substrate as a cavity and provides an opening part having a designated contour shape on the upper surface side of the substrate, a vibration transferring plate, which is bonded to the pressure chamber in a state that the vibration transferring plate covers the opening part, and a piezoelectric actuator, which is formed by layering a lower electrode, a piezoelectric plate, and an upper electrode on the vibration transferring plate, and includes the vibration transferring plate and a pressure chamber side wall, bonded to the vibration transferring plate, of the pressure chamber. And the designated contour shape of the opening part of the pressure chamber is a rectangle, and the length ratio of the short side to the long side of the rectangle is 0.8 or more and 1.0 or less, and the contour of the piezoelectric plate of the piezoelectric actuator is positioned within the contour shape of the opening part of the pressure chamber above the opening part.
According to a second aspect of the present invention, in the first aspect, the area of the piezoelectric plate is 0.5 or more and 1.0 or less of the area of the opening part of the pressure chamber.
According to a third aspect of the present invention, in the second aspect, the piezoelectric plate having the lower electrode is formed on the vibration transferring plate at the position where the center position of the piezoelectric plate is made to be almost equal to the center position of the opening part of the pressure chamber.
According to a fourth aspect of the present invention, in the third aspect, the contour of the piezoelectric plate is a rectangle.
According to a fifth aspect of the present invention, in the fourth aspect, the contour of the piezoelectric plate is a similarity rectangle to the contour shape of the opening part of the pressure chamber.
According to a sixth aspect of the present invention, in the fifth aspect, the contour of the piezoelectric plate is an almost equal shape to the contour shape of the opening part of the pressure chamber.
According to a seventh aspect of the present invention, in the third aspect, the contour of the piezoelectric plate is a circle.
According to an eighth aspect of the present invention, in the seventh aspect, at least a part of the circumference of the circular contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a ninth aspect of the present invention, in the seventh aspect, the circular contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a tenth aspect of the present invention, in the third aspect, the contour of the piezoelectric plate is an ellipse.
According to an eleventh aspect of the present invention, in the tenth aspect, at least a part of the ellipse contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a twelfth aspect of the present invention, in the tenth aspect, the ellipse contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a thirteenth aspect of the present invention, in the first aspect, the vibration transferring plate has a concave part or concave parts close to the edge part of the opening part of the pressure chamber.
According to a fourteenth aspect of the present invention, in the thirteenth aspect, the area of the concave part(s) is less than 0.5 of the area of the opening part of the pressure chamber.
According to a fifteenth aspect of the present invention, in the thirteenth aspect, the concave part(s) is a groove(s), which is formed along the contour of the vibration transferring plate in a state that the groove(s) is positioned at a place having a designated width from the contour of the vibration transferring plate.
According to a sixteenth aspect of the present invention, in the fifteenth aspect, the shape of the center part of the vibration transferring plate, surrounded by the groove, is a rectangle.
According to a seventeenth aspect of the present invention, in the fifteenth aspect, the shape of the center part of the vibration transferring plate, surrounded by the groove, is a circle or an ellipse.
According to an eighteenth aspect, in the thirteenth aspect, the grooves are formed at least four positions being rotation symmetry along the contour of the vibration transferring plate.
According to a nineteenth aspect of the present invention, in the eighteenth aspect, the grooves are formed along each side of the vibration transferring plate on the surface, which is bonded to the pressure chamber, of the vibration transferring plate.
According to a twentieth aspect of the present invention, in the eighteenth aspect, the grooves are formed in a  shape along each corner of the vibration transferring plate on the surface, which is bonded to the pressure chamber, of the vibration transferring plate.
According to a twenty-first aspect of the present invention, in the thirteenth aspect, a part or plural parts of the concave part(s) are connected to an ink supplying hole in the pressure chamber.
According to a twenty-second aspect of the present invention, there is provided a piezoelectric actuator for an ink jet printer head. The piezoelectric actuator for the ink jet printer head provides an upper electrode, a lower electrode, a piezoelectric plate disposed between the upper and lower electrodes, a vibration transferring plate bonded to the piezoelectric plate having the lower electrode, and a pressure chamber side wall being a part of a pressure chamber and bonded to the vibration transferring plate. And an opening part, which is covered with the vibration transferring plate, of the pressure chamber is a rectangle, and the length ratio of the short side to the long side of the rectangle is 0.8 or more and 1.0 or less, and the piezoelectric plate having the lower electrode is bonded to the vibration transferring plate within the contour of the opening part of the pressure chamber above the opening part.
According to a twenty-third aspect of the present invention, in the twenty-second aspect, the area of the piezoelectric plate is 0.5 or more and 1.0 or less of the area of the opening part of the pressure chamber.
According to a twenty-fourth aspect of the present invention, in the twenty-third aspect, the piezoelectric plate having the lower electrode is formed on the vibration transferring plate at the position where the center position of the piezoelectric plate is made to be almost equal to the center position of the opening part of the pressure chamber.
According to a twenty-fifth aspect of the present invention, in the twenty-fourth aspect, the contour of the piezoelectric plate is a rectangle.
According to a twenty-sixth aspect of the present invention, in the twenty-fifth aspect, the contour of the piezoelectric plate is a similarity rectangle to the contour shape of the opening part of the pressure chamber.
According to a twenty-seventh aspect of the present invention, in the twenty-sixth aspect, the contour of the piezoelectric plate is an almost equal shape to the contour shape of the opening part of the pressure chamber.
According to a twenty-eighth aspect of the present invention, in the twenty-fourth aspect, the contour of the piezoelectric plate is a circle.
According to a twenty-ninth aspect of the present invention, in the twenty-eighth aspect, at least a part of the circumference of the circular contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a thirtieth aspect of the present invention, in the twenty-eighth aspect, the circular contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a thirty-first aspect of the present invention, in the twenty-fourth aspect, the contour of the piezoelectric plate is an ellipse.
According to a thirty-second aspect of the present invention, in the thirty-first aspect, at least a part of the ellipse contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a thirty-third aspect of the present invention, in the thirty-first aspect, the ellipse contour of the piezoelectric plate having the lower electrode is positioned within the contour shape of the opening part of the pressure chamber, by disposing the vibration transferring plate between the piezoelectric plate having the lower electrode and the pressure chamber.
According to a thirty-fourth aspect of the present invention, in the twenty-second aspect, the vibration transferring plate has a concave part or concave parts close to the edge part of the opening part of the pressure chamber.
According to a thirty-fifth aspect of the present invention, in the thirty-fourth aspect, the area of the concave part(s) is less than 0.5 of the area of the opening part of the pressure chamber.
According to a thirty-sixth aspect of the present invention, in the thirty-fourth aspect, the concave part(s) is a groove(s), which is formed along the contour of the vibration transferring plate in a state that the groove(s) is positioned at a place having a designated width from the contour of the vibration transferring plate.
According to a thirty-seventh aspect of the present invention, in the thirty-sixth aspect, the shape of the center part of the vibration transferring plate, surrounded by the groove, is a rectangle.
According to a thirty-eighth aspect of the present invention, in the thirty-sixth aspect, the shape of the center part of the vibration transferring plate, surrounded by the groove, is a circle or an ellipse.
According to thirty-ninth aspect of the present invention, in the thirty-fourth aspect, the grooves are formed at least four positions being rotation symmetry along the contour of the vibration transferring plate.
According to a fortieth aspect of the present invention, in the thirty-ninth aspect, the grooves are formed along each side of the vibration transferring plate on the surface, which is bonded to the pressure chamber, of the vibration transferring plate.
According to a forty-first aspect of the present invention, in the thirty-ninth aspect, the grooves are formed in a  shape along each corner of the vibration transferring plate on the surface, which is bonded to the pressure chamber, of the vibration transferring plate.
According to a forty-second aspect of the present invention, in the thirty-fourth aspect, a part or plural parts of the concave part(s) are connected to an ink supplying hole in the pressure chamber.